[PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[Zhang Rui <rui.zhang@intel.com>]

Some buggy BIOS exports multiple ACPI video bus devices for the same
VGA controller, and multiple backlight control methods as well.
This may mess up the ACPI video backlight control.
http://bugzilla.kernel.org/show_bug.cgi?id=13577

We should at least send out a warning message in this case.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
 drivers/acpi/video.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Index: linux-2.6/drivers/acpi/video.c
===================================================================
--- linux-2.6.orig/drivers/acpi/video.c
+++ linux-2.6/drivers/acpi/video.c
@@ -2233,12 +2233,36 @@ static int acpi_video_resume(struct acpi
 	return AE_OK;
 }
 
+static acpi_status
+acpi_video_bus_match(acpi_handle handle, u32 level, void *context,
+			void **return_value)
+{
+	struct acpi_device *device = context;
+	struct acpi_device *sibling;
+	int result;
+
+	if (handle == device->handle)
+		return AE_CTRL_TERMINATE;
+
+	result = acpi_bus_get_device(handle, &sibling);
+	if (result)
+		return AE_OK;
+
+	if (!strcmp(acpi_device_name(sibling), ACPI_VIDEO_BUS_NAME))
+		printk(KERN_WARNING FW_BUG "Duplicate ACPI video bus "
+				"devices for the same VGA controller\n");
+	return AE_OK;
+}
+
 static int acpi_video_bus_add(struct acpi_device *device)
 {
 	struct acpi_video_bus *video;
 	struct input_dev *input;
 	int error;
 
+	acpi_walk_namespace(ACPI_TYPE_DEVICE, device->parent->handle,
+			    1, acpi_video_bus_match, device, NULL);
+
 	video = kzalloc(sizeof(struct acpi_video_bus), GFP_KERNEL);
 	if (!video)
 		return -ENOMEM;